A variety of circumstances may exist in computer systems and other systems in which it is desirable to use a “human test” to determine whether a communication originates with a human being or with a computer program that imitates a human being. For example, it may be desirable for a provider of a computer-related service that is intended for use by individual users, i.e. by human beings, to determine whether the computer-related service is being accessed by a computer program that imitates a human being.
A computer program that imitates a human being in the context of web communication is commonly referred to as a “bot” which is a shortened version of “robot.” Examples of computer-related services that may be intended for use by individual users in the context of web-based communication include email services, personal web page services, personal data storage services, web access accounts, etc.
An unscrupulous party may employ bots to create numerous user accounts with a computer-related service that is intended for individual users. For example, an unscrupulous party may use bots to create numerous user accounts with a free email service and then use the obtained email accounts for mass mailings of spam. Similarly, an unscrupulous party may use bots to create numerous free personal web page accounts and then store large volumes of information on the obtained web storage space.
A provider of a computer-related service may attempt to prevent creation of user accounts by bots by generating a registration form that includes a human test. A prior human test may include an image of a decimal number in a stylized fashion along with a request that the represented number be entered into a form field. Such a prior human test relies on the human capability to recognize stylized numbers. Unfortunately, a bot may employ optical character recognition (OCR) techniques to defeat a human test that relies on number recognition.